Aircraft prognostic systems and methods for determining adaptive time between overhaul for line replaceable units

ABSTRACT

Prognostic systems and methods for providing adaptive Time Between Overhaul (TBO) value for one or more Line Replaceable Units (LRUs) are provided. In one embodiment, the LRU prognostic system includes a first LRU, an aircraft position data source configured to monitor the position of an aircraft carrying the LRU prognostic system, and a controller coupled to the first LRU and to the aircraft position data source. The controller is configured to: (i) estimate the degradation of the first LRU based at least in part on the duration of time the aircraft position resides in any one of a plurality of different environmental zones while the aircraft is operational, and (ii) calculate an adaptive TBO value for the first LRU utilizing the estimated LRU degradation.

TECHNICAL FIELD

The present invention relates generally to aircraft and, moreparticularly, aircraft prognostic systems and methods for determiningadaptive Time Between Overall (TBO) values for one or more linereplaceable units.

BACKGROUND

Modern aircraft are commonly equipped with a relatively large number ofLine Replaceable Units (LRUs), which perform various functionssupporting aircraft operation. By definition, LRUs are modularcomponents that can be removed and replaced in-field in a relativelyefficient manner to, for example, minimize downtime of the aircraftduring maintenance, such as during an unplanned maintenance event andrepair. To reduce the likelihood of in-field LRU failure, LRUs are oftenreplaced and overhauled after expiration of a so-called “Time BetweenOverhaul” or “TBO” value assigned to the LRU. The TBO value is a fixedperiod, which is typically measured in flight hours and set by theOriginal Equipment Manufacturer (OEM) during initial design of the LRU.The OEM may determine the TBO value of a particular LRU based upon anumber of different factors. These factors may include the structuralcharacteristics of the LRU (e.g., the base materials of the LRU, thepresence of rubber seals and gaskets, the provision of coatings orcoating systems, etc.), the mechanical stressors to which the LRU may beexposed (e.g., expected vibration and stress concentrations), and therange of operational environments in which the LRU may potentially bedeployed.

BRIEF SUMMARY

Embodiments of a Line Replaceable Unit (LRU) prognostic system areprovided. In one embodiment, the LRU prognostic system includes a firstLRU, an aircraft position data source configured to monitor the positionof an aircraft carrying the LRU prognostic system, and a controllercoupled to the first LRU and to the aircraft position data source. Thecontroller is configured to: (i) estimate the degradation of the firstLRU based at least in part on the duration of time the aircraft positionresides in any one of a plurality of different environmental zones whilethe aircraft is operational, and (ii) calculate an adaptive Time BetweenOverhaul (TBO) value for the first LRU utilizing the estimated LRUdegradation.

In a further embodiment, the LRU prognostic system includes a first LRUand a Radio Frequency Identification (RFID) module, which is embeddedwithin or otherwise affixed to the first LRU. The RFID module containsan LRU memory, which stores a baseline TBO value, degradation ratescorresponding to a plurality of different environmental zones, anadaptive TBO value, and possibly other LRU usage-related data. The LRUprognostic system further includes a calculation sub-system coupled tothe first RFID module. The calculation sub-system is configured toperiodically update the adaptive TBO value by estimating the degradationof the first LRU based at least in part on the duration of time theaircraft position is located in the plurality of different environmentalzones and the degradation rates associated therewith, as recalled fromthe RFID module. Additionally, the calculation sub-system calculates anew adaptive TBO value from the estimated LRU degradation and thenstores the new adaptive TBO value in the LRU memory. This process can berepeated to periodically update the adaptive TBO value at predeterminedintervals or events, such as each time the LRU has been operated inflight.

Further provided are embodiments of a method for determining an adaptiveTBO value for a first LRU. The method is carried-out by the controllerof a LRU prognostic system deployed onboard an aircraft. In anembodiment, the method includes the step or process of estimating, atthe controller, the degradation of the first LRU based at least in parton the duration of time the aircraft position resides in any one of aplurality of different environmental zones. Further, the adaptive TBOvalue for the first LRU is calculated at the controller utilizing theestimated LRU degradation.

BRIEF DESCRIPTION OF THE DRAWINGS

At least one example of the present invention will hereinafter bedescribed in conjunction with the following figures, wherein likenumerals denote like elements, and:

FIG. 1 is a block diagram of a Line Replaceable Unit (LRU) prognosticsystem, as illustrated in accordance with an exemplary embodiment of thepresent invention;

FIG. 2 is an operative use spectrum illustrating an exemplary manner inwhich the adaptive TBO value for one or more LRUs can be adjustedrelative to a baseline TBO value based, at least in part, upon theenvironmental exposure of an aircraft carrying the LRU(s);

FIG. 3 is an isometric view of a rotary wing aircraft including aplurality of LRUs having Radio Frequency Identification (RFID) modulesembedded therein, which can further be included in an exemplaryimplementation of the LRU prognostic system shown in FIG. 1; and

FIGS. 4, 5, and 6 are schematic diagrams illustrating operation of theLRU prognostic system shown in FIGS. 1 and 3 in aircraft start-up,in-flight, and aircraft shut-down modes, respectively, as illustrated inaccordance with a further exemplary embodiment of the present invention.

DETAILED DESCRIPTION

The following Detailed Description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by any theorypresented in the preceding Background or the following DetailedDescription.

As noted in the foregoing section entitled “BACKGROUND,” a LineReplaceable Unit (LRU) is commonly assigned a fixed Time BetweenOverhaul (TBO) value or period by the Original Equipment Manufacturer(OEM) during the initial design stage of the LRU. As the OEM lacks priorknowledge of the particular environmental conditions to which the LRUwill be exposed over its impending service life, the OEM will typicallyset the TBO value based upon an anticipated range of operationalconditions to which the LRU may reasonably be subjected. This practiceof setting a fixed LRU TBO value, which does not change or adapt inrelation to the actual environmental exposure of the LRU, can result inan unnecessary increase in maintenance costs, can contribute to aninefficient scheduling of inspections, and can negatively impact LRUreliability and, therefore, the overall reliability of the largeraircraft systems. Consider, for example, a scenario in which anLRU-equipped aircraft operates primarily or exclusively in mildenvironmental conditions, such as high humidity or ice-rich conditions.In this case, the LRUs carried by the aircraft may be subject to arelatively low rate of environmental degradation and, thus, be capableof providing useful service life well beyond the fixed TBO valueassigned by the OEM. Consequently, replacement of the LRUs uponexpiration of the manufacturer-set TBO value thus incurs unneededmaintenance costs and can contribute to inefficient or sub-optimalmaintenance scheduling. Conversely, in instances wherein theLRU-equipped aircraft primarily or exclusively operates in exceptionallyharsh environmental conditions, such as high salinity or coastalconditions, replacement of the LRUs prior to the expiration of theirrespective manufacturer-set TBO values may be warranted. In suchinstances, there may exist an undesirably high probability of LRUfailure immediately prior to expiration of the fixed manufacturer-setTBO thereby decreasing the overall reliability of the aircraft systems.Further complicating this problem is the fact that a single LRU can bedeployed on multiple different aircraft over the lifespan of the LRUthus losing the essence of environmental degradation factor affectingthe TBO.

To overcome the above-described limitations associated with the usage ofa fixed or manufacturer-set TBO values, the following describes aircraftprognostic systems and methods enabling a variable or “adaptive” TBOvalue to be calculated an for one or more LRUs deployed onboard anaircraft and periodically updated at predetermined intervals or uponoccurrence of a particular event, such as upon completion of a flightoperation. The adaptive TBO value may be derived from a baseline TBOvalue, such a manufacturer-set TBO value, which is adjusted based uponan estimated degradation of the LRU. The estimated degradation of theLRU can be determined, in turn, by monitoring the cumulative period oftime the aircraft resides in any one of a plurality of differentgeographically-divided zones, each having a particular LRU degradationrate associated therewith. The environmental degradation ratescorrelated to the geographical zones may be LRU-specific and recalledfrom a memory embedded in the LRU. Additionally, in certain embodiments,the degradation rates can be adjusted based upon sensor input monitoringthe health of the LRU. The adaptive TBO value may then be stored on, forexample, memories affixed to each LRU and, preferably, memories includedin Radio Frequency Identification (RFID) devices embedded into each LRU.In this manner, the adaptive TBO value can be readily retrieved from theLRU even in instances wherein the LRU is deployed on multiple differentaircraft over its operational lifespan. The adaptive TBO value can beupdated at a relatively rapid refresh rate or upon occurrence of aparticular event (e.g., aircraft shutdown) to ensure that the TBO valuereflects the actual environmental exposure of the LRU in real-time ornear real-time.

FIG. 1 is a schematic of an LRU prognostic system 10 deployed onboard anaircraft, such as a rotary wing aircraft, as illustrated in accordancewith an exemplary embodiment of the present invention. LRU prognosticsystem 10 includes a calculation sub-system 12, a first LRU 14, and anynumber of additional LRUs (indicated FIG. 1 by symbol 16). LRUprognostic system 10 can include or be utilized in conjunction withvarious different types of LRUs. A non-exhaustive list of LRUs suitablefor usage within system 10 includes certain engines, transmission units,heat exchangers, pumps (e.g., oil pumps, fuel pumps and fuel controls,etc.), cooling fans, valves (e.g., surge control valves, fuel meteringvalves, bleed air valves, etc.), starter motors, etc.), ignition controlunits, and wiring harnesses. LRU prognostic system 10 is advantageouslydeployed onboard a rotary wing aircraft or helicopter, but may also bedeployed onboard a fixed wing aircraft.

In the exemplary embodiment illustrated in FIG. 1, LRU 14 includes aRadio Frequency Identification (RFID) module 18 (also commonly referredto as an “RFID tag”). RFID module 18 may be affixed to the housing ofLRU 14 during original manufacture or as a retrofit installation; theterm “affixed” encompassing mounting of the RFID module 18 to theexterior of LRU 14, as well as integration or embedment of RFID module18 within LRU 14. RFID module 18 contains an RFID antenna 20, whichallows wireless bi-directional communication with an LRU memory 22further contained within module 18. LRU memory 22 can assume any formsuitable for storing data of the type described below. LRU memory 22 isconveniently implemented as a solid state, non-volatile memory, such asflash memory. In one embodiment, memory 22 is realized utilizingElectrically Erasable Programmable Read-Only Memory (EEPROM). In theillustrated example, RFID module 18 is passive and, thus, utilizes theenergy obtained from a read/write signal or interrogation to perform thedesired actions. However, in further embodiments, RFID module 18 can beactive and may include a power source (not shown), such as a powerstorage device (e.g., a battery or super capacitor), an energyharvesting device, or a wired connection to the LRU power feed.

As schematically indicated in FIG. 1, LRU memory 22 is preferably storesat least three different types of data pertaining to embodiments of thepresent invention: (i) baseline TBO value 26, (ii) degradation rates 28assigned to a plurality of different environmental zones, and (iii) anadaptive TBO value 30. Each of these different types of data can bestored in a separate sector or area of memory 22; however, this need notalways be the case. Baseline TBO value 26 is a fixed or constant TBOvalue, which may be set by the OEM or another entity during originalmanufacture of LRU 14. Degradation rates 28 represent different rates ofdegradation that are assigned to a number of environmental zones. Forexample, a first degradation rate of D₁ may be assigned to a highsalinity environment, a second degradation rate of D₂ may be assigned toa high humidity environment (with D₂ being less than D₁), and so on.Here, it will be noted that the environmental zones degradation ratesmay be specific to LRU 14; and a different type of LRU included insystem 10 may have a different set of environmental zone degradationrates associated therewith. Finally, adaptive TBO value 30 representsthe TBO value calculated for LRU 14 based upon the estimated degradationand actual environmental of LRU 14. TBO value 30 can be calculated as afunction of the baseline TBO value, the amount of time the aircraftoperates in a particular environmental zone or zones, and thedegradation rates associated with those zone(s), as described below. Itwill be appreciated that LRU memory 22 can also store other data (e.g.,maintenance log information) in addition to baseline TBO value 26,degradation rates 28, and adaptive TBO value 30 in some implementations.

With continued reference to the exemplary embodiment shown in FIG. 1,calculation sub-system 12 includes a controller 32, an RF transceiver 34having an RF antenna 36, an aircraft position data source 38, and anenvironmental zone database 40. Additionally, in certain embodiments,calculation sub-system 12 may include one or more sensors 42 formonitoring parameters pertaining to the health or degradation of LRU 14.Controller 32 can include any suitable number of individualmicroprocessors, microcontrollers, digital signal processors, programmedarrays, and other standard components known in the art. Controller 32may include or cooperate with any number of software or firmwareprograms designed to carry out the various methods, process tasks,calculations, and control functions described herein. RFID transceiver34 can assume any form enabling wireless communication with antenna 20of RFID module 18, preferably over an Ultra High Frequency (UHF)bandwidth. Aircraft position data source 38 can assume any form suitablefor tracking aircraft position, such as a Global Positioning System(GPS). Finally, when present, sensor(s) 42 can be any type of sensorsuitable for measuring parameters contributing to LRU degradation orhealth, such as vibration sensors, temperature sensors, chemicalsensors, wear sensors, and the like. While illustrated as part ofsub-system 12 in FIG. 1, it will be appreciated that sensor(s) 42 can beattached to or embedded within LRU 14 in further embodiments.

As indicated in FIG. 1 by graphic 44, environmental zone database 40stores information correlating a wide range of geographic positions orcoordinates (latitude and longitude) to a number of differentenvironmental zones having disparate influences on the degradation rateof LRU 14 and the other LRUs included in system 10 (see FIG. 3). Theinformation in database 40 can be stored as, for example, a map or atwo-dimensional look-up table, which encompasses the operational rangeof the aircraft. As previously stated, the environmental zones arepreferably classified by environmental characteristics affecting(accelerating or decelerating) the rate of LRU degradation. Examples ofdifferent environmental zones that may have varying effects on LRUdegradation rates are saline, high humidity, desert, hot zones, andice-rich zones, to list but a few examples.

During operation of LRU prognostic system 10, controller 32 periodicallycalculates an adaptive TBO value for LRU 14 and any other LRUs includedin prognostic system 10. For ease of explanation, the followingdescription will focus primarily on the manner in which prognosticsystem 10 determines the adaptive TBO value for LRU 14. It will beappreciated, however, that prognostic system 10 can simultaneouslydetermine the adaptive TBO value for any number of additional LRUsutilizing the process described herein, such as the other LRUs shown inFIG. 3 (described below). In general, controller 32 of LRU prognosticsystem 10 will calculate the adaptive TBO value for LRU 14 utilizing anestimated LRU degradation value, which is determined, based at least inpart, on the duration of time the aircraft position resides in any oneof a plurality of different environmental zones while the aircraft isoperational. Controller 32 preferably estimates the degradation of thefirst LRU as a function of duration of time the aircraft position islocated in the plurality of different environmental zones and thedegradation rates corresponding to those zone(s), as recalled from LRUmemory 22. The duration of time LRU 14 and, more generally, the aircraftcarrying LRU 14 is located in each of the environmental zones can bedetermined by correlating the aircraft position (as monitored byaircraft position data source 38) with the plurality of differentenvironmental zones (as stored in environmental zone database 40), asfurther described below in conjunction with FIG. 5.

FIG. 2 is an LRU usage spectrum 50 generally illustrating the manner inwhich the adaptive TBO value varies depending upon the operatingenvironment of the aircraft carrying LRU 14 and any other LRUs includedwithin system 10. LRU usage spectrum 50 is divided into three segments:(i) a minimal operating segment 52, which is characterized by operationin relatively mild environmental conditions; (ii) a normal operatingsegment 54, which is characterized by operation in moderate to slightlyharsh environmental conditions; and (iii) an extreme operating segment56, which is characterized by operation in harsh environmentalconditions. In an embodiment wherein the baseline TBO value of LRU 14is, for example, 2000 flight hours, the adaptive TBO value stored in LRUmemory 22 may initially be equivalent to the baseline TBO value. If theaircraft carrying LRU 14 is operated primary or exclusively in anenvironment having an accelerated degradation factor connectedtherewith, such as a saline environment, the adaptive TBO value willgradually decrease relative to the baseline TBO value. For example, theadaptive TBO value may call for replacement of the LRU 14 at 1500 flighthours. By replacing LRU 14 at this time, the reliability of LRU 14 maybe increased, as indicated in the lower right portion of FIG. 2. Toprovide a contrasting example, if the aircraft carrying LRU 14 isoperated primary or exclusively in an environment having a decelerateddegradation factor, such as a high humidity or ice-rich environment, theadaptive TBO value will gradually increase relative to the baseline TBOvalue. For example, the adaptive TBO value may call for replacement ofthe LRU 14 at 2500 flight hours. By replacing LRU 14 in accordance withthe adaptive TBO value, which is extended relative to the baseline TBOvalue, premature replacement of LRU 14 is avoided thereby reducing costand the performance of unneeded maintenance, as indicated in the lowerright portion of FIG. 2.

In actual implementations, LRU prognostic system 10 will typicallyinclude a relatively large number of LRUs in which both passive andactive RFID modules or tags are embedded. Furthermore, various differentarchitectures can be utilized enabling communication between thecalculation sub-system 12 and RFID module 18. For example, acommunication gateway can be utilized to facilitate communicationbetween sub-system 12, RFID module 18 on LRU 14, and the RFID modulescontained with any other non-illustrated LRUs included in system 10.Further emphasizing this point, FIG. 3 is an isometric view of a rotarywing aircraft 46 (partially shown) equipped with an LRU prognosticsystem, which may be considered an implementation of LRU prognosticsystem 10 (FIG. 1) for purposes of the following description. In theimplementation shown in FIG. 3, the LRU prognostic system includes areader or antenna (represented by a first symbol in key 48), a dataconcentrator or gateway (represented by a second symbol in key 48), anda number of passive and active RFID modules (represented by third andfourth symbols in key 48, respectively) distributed throughout theaircraft. The LRU prognostic system may also include a mesh network anda number of wireless connections, as further indicated by key 48. Rotarywing aircraft 46 includes a relatively large number of LRUs containingembedded RFID tags and may consequently be referred to as an “RFIDenabled aircraft.”

In the embodiment shown in FIG. 3, the degradation of LRUs can becalculated in real time and stored in the memories of the respective LRUtags in the following manner. As indicated above, there may be severalread/write devices installed throughout aircraft 46 to provideread/write facilities to the RFID modules via a wireless communicationmode. The read/write devices can be connected to the gateway via thewireless (e.g., RF) connection shown in FIG. 3. In a preferredembodiment, the gateway is the only mechanism connected to an externalmode in a wireless Local Area Network (LAN), via Ethernet, or viaanother connection. The calculation sub-system (e.g., sub-system 12shown in FIG. 1) can likewise be connected to gateway wirelessly or viaan Ethernet connection. As noted above, each LRU RFID tag may containthree distinct storages or memory sectors. A first memory sector storesdegradation rates of the LRU under different environmental conditions,such as saline, desert, high humidity, ice operation, and the like. Thesecond memory sector stores the baseline TBO, which may be set by themanufacturer. The third memory sector may store the adaptive TBO. Theadaptive TBO may initially be equivalent to the baseline TBO and changeover the operational lifespan of the LRU in accordance with an algorithmhosted by calculation sub-system 12 (FIG. 1), as generally describedbelow in conjunction with FIGS. 4-6.

By way of non-limiting example, controller 32 of LRU prognostic system10 can updates the adaptive TBO value for each LRU utilizing a threestage process. The first stage occurs during power-up or start-up of theaircraft, the stage second occurs during flight of the aircraft, and thethird stage occurs during aircraft shut down. The first, second, andthird stages are illustrated conceptually in FIGS. 4-6, respectively.Referring initially to FIG. 4, during the first stage (aircraft start-upcondition), controller 32 initially retrieves the current aircraftposition and start-up time of the aircraft from aircraft position datasource 38 (BLOCKS 60 and 62). In an embodiment wherein position datasource 38 is an aircraft GPS, controller 32 can directly retrieve thisinformation from the GPS device or avionics. Afterwards, controller 32recalls the coordination of aircraft position and environmental zonesfrom environmental zone database 40. Controller 32 then identifies theenvironmental zone corresponding to the present aircraft position fromthe data recalled from environmental zone database 40 (BLOCK 68).

FIG. 5 illustrates the second stage or operational mode (in-flightcondition) in which controller 32 of LRU prognostic system 10 (FIG. 1)may operate. During this stage, controller 32 periodically retrievesaircraft position and time data from aircraft position data source 38(BLOCKS 72 and 74), which, again, may be a GPS device. Controller 32then compares the updated aircraft position data to theposition-to-environmental zone data stored in environmental zonedatabase 40 to determine whether the aircraft remains in thepreviously-identified environmental zone or has transitioned into a newenvironmental zone. Utilizing this information, the calculationsub-system 12 then determines the cumulative time period of the aircraftand, therefore, the LRU or LRUs contained within LRU prognostic system10 (FIG. 1) resides in or is operated in each environmental zone (BLOCKs76 and 78).

The third and final stage of the process carried-out by controller 32(FIG. 1) will typically occur after landing during shut down of theaircraft. During this stage, calculation sub-system 12 performs thefollowing steps conceptually illustrated in FIG. 6. First, calculationsub-system 12 forwards a request to gateway 82 to fetch (read data) theLRU-specific degradation rates and adaptive TBO value from each LRU(identified as 86(a)-(f) in FIG. 6). After this data has been recalled,calculation sub-system 12 may create zonal map or table. The calculationsub-system 12 then utilizes this map or table, along with thepreviously-determined cumulative time period the aircraft positionresides in different environmental zones while operational, to calculatea new adaptive TBO value 90 for each LRU 86(a)-(f). Finally, calculationsub-system 12 can forward request to gateway 82 to write the newadaptive TBO value to the memories contained within the respective LRUs'RFID modules 88(a)-(f) utilizing read/write devices 84(a)-(c). This caninclude, for example, memory 22 included in RFID module 18 of LRU 14shown in FIG. 1. As noted above, the zone-dependent degradation rates ofthe LRUs can be fixed by the manufacturer or operator. Alternatively,the degradation rates of LRUs 86(a)-(f) can be varied based upon theenvironmental conditions to which the aircraft is subjected. In this theregard, the degradation rates of LRUs 86(a)-(f) can be determined inreal time or near real time using LRU health data (e.g., wear, torque,moments, power and contamination of lubrication oil, and the like),environmental data (e.g., temperature, pressure, altitude, weather, andthe like), and flight data (e.g., aerodynamic forces, vibration, speed,and the like) obtained from sensors onboard the aircraft, such assensors 42 shown in FIG. 1.

When it is desired to retrieve the updated TBO value from the LRU orLRUs included in LRU prognostic system 10 (FIG. 1), the memoriescontained with the RFID tags can be accessed through controller 32, agateway device (FIG. 3), or another intermediary device. Alternatively,the memories contained within the RFID tags can be accessed directlyutilizing either wireless connection or a physical interface. Inpreferred implementations, a technician utilizes an RFID scanner toaccess the RFID memories directly, a RFID scanner. The term “RFIDscanner,” as appearing herein, encompasses dedicated handheld devices,RFID-compatible smart phones, RFID-enabled tablet and laptop computers,and any other device capable of wirelessly receiving data from an RFIDmodule in the manner described herein. An example of a dedicated RFIDscanner suitable for usage in the below-described process is theINTERMEC-brand reader commercially marketed by Honeywell Scanning andMobility. In certain embodiments, the range of RFID antenna 20 (FIG. 1)may be intentionally limited to a relatively small radius (e.g., on theorder of 1-2 meters) to reduce the likelihood of inadvertent receptionby a passenger's mobile phone or other unauthorized device.

The foregoing has thus provided embodiments of an aircraft prognosticsystem that functions to establish an adaptive TBO value for one or moreLRUs. In an embodiment, the aircraft prognostic system monitors thecumulative period of time the aircraft operates in any one of aplurality of different geographically-divided zones, each of which has aparticular LRU degradation rate associated therewith. The environmentaldegradation rates correlated to the geographical zones may beLRU-specific and recalled from a memory embedded in the LRU.Additionally, in certain embodiments, the degradation rates can beadjusted based upon sensor data estimating the degradation of the LRU.The adaptive TBO value may then be stored on, for example, memoriesaffixed to each LRU and, preferably, memories included in RFID modulesembedded into each LRU. In this manner, the adaptive TBO value can bereadily retrieved from the LRU even in instances wherein the LRU isdeployed on multiple different aircraft over its operational lifespan.

While at least one exemplary embodiment has been presented in theforegoing Detailed Description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing Detailed Description willprovide those skilled in the art with a convenient road map forimplementing an exemplary embodiment of the invention. It beingunderstood that various changes may be made in the function andarrangement of elements described in an exemplary embodiment withoutdeparting from the scope of the invention as set-forth in the appendedclaims.

1. (canceled)
 2. The LRU prognostic system of claim 6 further comprisinga memory storing degradation rates for the plurality of differentenvironmental zones, the controller configured to estimate thedegradation of the first LRU as a function of duration of time theaircraft position resides in the plurality of different environmentalzones and the corresponding degradation rates.
 3. The LRU prognosticsystem of claim 2 wherein the memory is embedded in the first LRU. 4.The LRU prognostic system of claim 2 further comprising a sensorconfigured to monitor a parameter affecting the degradation rate of thefirst LRU, the controller coupled to the sensor and configured to varyone or more of the degradation rates stored in the memory based upondata provided by the sensor.
 5. (canceled)
 6. A Line Replaceable Unit(LRU) prognostic system, comprising: a first LRU: an aircraft positiondata source configured to monitor a position of an aircraft carrying theLRU prognostic system; an environmental zone database storing a range ofaircraft positions correlated with a plurality of differentenvironmental zones and further storing degradation rates for at leastone of a group consisting of a high humidity zone, a desert zone, asaline zone, and an ice-rich zone; and a controller coupled to the firstLRU, to the aircraft position data source, and to the environmental zonedatabase, the controller configured to: (i) estimate a degradation ofthe first LRU based, at least in part, on a duration of time theaircraft position resides in one or more of the plurality of differentenvironmental zones while the aircraft is operational, as determinedutilizing aircraft position and the environmental zone database, and(ii) calculate an adaptive Time Between Overhaul (TBO) value for thefirst LRU utilizing the estimated LRU degradation.
 7. The LRU prognosticsystem of claim 6 further comprising an LRU memory affixed to the firstLRU, the controller coupled to the LRU memory and further configured tostore the adaptive TBO value in the LRU memory.
 8. The LRU prognosticsystem of claim 7 further comprising: a Radio Frequency Identification(RFID) module embedded in the first LRU and containing the LRU memory;and an RF transceiver coupled to the controller and enabling wirelesscommunication with the RFID module.
 9. The LRU prognostic system ofclaim 7 wherein the controller is operable in a shutdown mode duringwhich the controller updates the adaptive TBO value during shutdown ofthe aircraft.
 10. The LRU prognostic system of claim 7 wherein the LRUmemory further stores a baseline TBO value therein, and wherein thecontroller is configured to determine the adaptive TBO value from thebaseline TBO value and the estimated LRU degradation.
 11. The LRUprognostic system of claim 6 wherein the controller is operable in apower-up mode during which the controller determines the presentaircraft position and current time from the aircraft position datasource.
 12. The LRU prognostic system of claim 11 wherein the controlleris further operable in an in-flight mode during which controllerperiodically: (i) determines the present aircraft position and currenttime from the aircraft position data source, and (ii) calculates acumulative time period during which the aircraft resides in theplurality of different environmental zones.
 13. A Line Replaceable Unit(LRU) prognostic system deployable on an aircraft, the LRU prognosticsystem comprising: a first LRU; a first Radio Frequency Identification(RFID) module affixed to the first LRU, the first RFID module containingan LRU memory storing a baseline Time Between Overhaul (TBO) value, LRUdegradation rates corresponding to a plurality of differentenvironmental zones, and an adaptive TBO value; and a calculationsub-system coupled to the first RFID module and configured toperiodically update the adaptive TBO value by: (i) estimating adegradation of the first LRU based at least in part on a duration oftime an aircraft position resides in the plurality of differentenvironmental zones and LRU degradation rates associated with theplurality of different environmental zones, as recalled from the RFIDmodule, (ii) calculating a new adaptive TBO value from the estimated LRUdegradation, and (iii) storing the new adaptive TBO value in the LRUmemory.
 14. The LRU prognostic system of claim 13 wherein thecalculation sub-system is configured to update the adaptive TBO value inresponse to shut-down of the aircraft.
 15. The LRU prognostic system ofclaim 13 wherein the calculation sub-system comprises: a GlobalPositioning System (GPS) device configured to monitor a current aircraftposition; an environmental zone database storing information correlatingthe plurality of different environmental zones with a range of aircraftpositions; and a controller coupled to the GPS device and to theenvironmental zone database, the controller configured to determine theduration of time the aircraft position is located in the plurality ofdifferent environmental zones by periodically comparing the currentaircraft position with the information stored in the environmental zonedatabase.
 16. The LRU prognostic system of claim 13 further comprising:a second LRU; and a second RFID module affixed to the second LRU andcontaining a second LRU memory storing a second baseline TBO value forthe second LRU, LRU degradation rates corresponding to the plurality ofdifferent environmental zones for the second LRU, and a second adaptiveTBO value for the second LRU; wherein the controller is coupled to thesecond RFID module and is further configured to periodically update thesecond adaptive TBO value stored in the second LRU memory of the secondLRU.
 17. The LRU prognostic system of claim 16 further comprising agateway device through which the calculation sub-system wirelesslycommunicates with the first RFID module and the second RFID module. 18.The LRU prognostic system of claim 16 wherein the LRU degradation ratesstored in the second RFID module differ relative to the LRU degradationrates stored in the first RFID module. 19.-20.(canceled)
 21. A LineReplaceable Unit (LRU) prognostic system, comprising: a first LRU; anaircraft position data source configured to monitor a position of anaircraft carrying the LRU prognostic system; a controller coupled to thefirst LRU and to the RF transceiver, the controller configured to: (i)estimate a degradation of the first LRU based, at least in part, on aduration of time the aircraft position resides in at least one of aplurality of different environmental zones while the aircraft isoperational, and (ii) calculate an adaptive Time Between Overhaul (TBO)value for the first LRU utilizing the estimated LRU degradation; and aRadio Frequency Identification (RFID) module affixed to the first LRU,the RFID module comprising: an LRU memory in which the adaptive TBOvalue is stored; and a first Radio Frequency (RF) transceiver enablingwireless communication with the RFID module.
 22. The LRU prognosticsystem of claim 21 wherein the RFID module is embedded within the firstLRU.
 23. The LRU prognostic system of claim 21 wherein the controller isfurther configured to estimate the degradation of the first LRUutilizing LRU degradation rates corresponding to the plurality ofdifferent environmental zones.
 24. The LRU prognostic system of claim 23wherein the LRU degradation rates are stored in the LRU memory of theRFID module.